Secretary of Defense Caspar W. Weinberger and Secretary of State George P. Shultz yesterday termed the installation of Soviet SA5 antiaircraft missiles in Syria and their manning by Soviet crews serious and dangerous.

Shultz, testifying before a Senate Appropriations subcommittee, said the Soviet action is "a sobering, destabilizing event" that is "not welcome," and said the United States has "stated that to the Soviet Union."

Weinberger, appearing on the NBC-TV "Today" show, said the presence of the long-range missiles and their Soviet crews created "a very serious" situation that increases the danger of new fighting in the Middle East and shows that Syria "is just another outpost of the Soviet empire."

The installation of the SA5s marks the first time that these missiles have been deployed outside Soviet borders.

The missiles are believed to be capable of hitting aircraft flying at medium and high altitudes at distances of up to 150 miles away, which means that they could threaten Israeli aircraft over Lebanon or even American aircraft operating from carriers in the Mediterranean.

During Israel's invasion of Lebanon last summer, the Israelis wiped out an array of Soviet-supplied antiaircraft missiles that had been based in Lebanon and manned, presumably, by Syrian crews. The Soviets, western officials surmise, probably wanted to restore their image in the Middle East by deploying the new missiles.

There is concern that the Israelis may attack the new sites inside Syria in another flare-up, which could kill Soviet crews and provoke a military response from the new Soviet leader, Yuri V. Andropov.

A former official of the Reagan administration, Joseph Churba, told a news conference here yesterday that the Soviets may be trying to provoke a conflict with Israel in order to test their SA5 missiles and new tactics developed since the Israelis wiped out the other Soviet missiles last summer.

Churba, who resigned from the Arms Control and Disarmament Agency last summer, is the author of an open letter to President Reagan that appeared as a full-page advertisement in The New York Times on Sunday, signed by 130 retired generals and admirals. The letter urged the president to revitalize strategic military cooperation with Israel, which the signers claim has made extraordinary advances in tactics and weapons technology that can be used to defeat Soviet forces in any future conflict involving the United States.

The traditional exchange of information between the two countries has been interrupted because of disputes between Weinberger and former Israeli defense minister Ariel Sharon over Israeli terms for such exchanges.

Pentagon officials said that Weinberger, who gets along much better with Sharon's successor, Moshe Arens, has submitted a simpler alternative proposal on the exchange of secret military data, which the Israelis are considering.

In his senate testimony, Shultz also assailed the Senate's approval last week of a resolution calling upon the administration not to sell advanced weaponry to Jordan so long as that country continues to oppose the Camp David peace process and buys arms from Moscow.

Shultz said that the resolution would not be helpful in encouraging Jordan's ruler, King Hussein, to join the Middle East peace process, and added that the resolution's timing was distressing because of the installation of the SA5s in Syria, a nation that is not on good terms with Jordan.